Cutting tool

ABSTRACT

The invention relates to a cutting tool, in particular for the turning out of drillings, comprising a clamping piece ( 10 ) for fixing the tool in a clamp holder. Said clamping piece ( 10 ) comprises two clamping surfaces ( 30 ), which converge on each other in the direction of the one side ( 32 ) of the clamping piece ( 10 ) and in the direction of the other side ( 34 ) of the clamping piece ( 10 ) run into a roof-type surface ( 36 ) and, on the side of the clamping piece ( 10 ) facing away from the clamp holder, connect to a rod-like neck piece ( 12 ), which tapers in cross-section relative to the clamping piece ( 10 ) the free end of which is connected to a cutting piece ( 14 ) as one piece, provided with a cutting edge ( 16 ) on the external end thereof to which a face ( 18 ) of the cutting piece ( 14 ) connects in the direction of the neck piece ( 12 ). A high degree of reinforcement for the neck piece and the cutting piece arranged on the free end thereof with the blade or the blade edge thereof is achieved, whereby the neck piece ( 12 ) has two reinforcement pieces running along the same, transverse to the plane of the cutting edge ( 16 ), which are embodied in the manner of reinforcing ribs ( 20, 22 ) which convergently taper in the direction of the cutting piece ( 14 ), which are diametrically opposed in relation to the neck piece ( 12 ) and have the greatest width thereof at the point of transition into the clamping piece ( 10 ).

[0001] The invention relates to a cutting tool, in particular forhollowing drill holes, having a clamp component for securing the tool ina tool holder, a neck component tapered in cross-section relative to theclamp component adjoining on the side of the clamp component facing awayfrom the tool holder, and an integral cutting component provided at itsextremity with a cutting edge which adjoins a face of the cuttingcomponent in the direction of the neck component. A comparable cuttingtool is disclosed in EP-B-0 385 280. The solution disclosed relates toan inner cutter for machining the interior surface of drill holes, forexample, for cutting circumferential grooves into the drill hole wall,for precision machining of the drill hole wall by finish turning of thedrill hole wall, for thread cutting in a bore hole, and the like.

[0002] The cutting edge of the tool moves in a radial direction ofadvance during parting in machining the interior wall of a drill hole.In the process the cutting edge must be positioned with the greatestaccuracy possible in a diametral advance plane extending parallel tothis radial direction of advance. Only with the cutting edge in thisposition is an optimal clearance angle obtained. Spacing the cuttingedge away from the diametral advance plane results in clearance angleswhich may lead to unfavorable results in metal removal, such asvibration of the tool. For this reason very precise rotary positioningof the tool in the tool holder must be achieved, and the position of thetool must not vary appreciably when a load is applied to the tool.Distances between the cutting edge and this diametral plane areespecially critical in the case of drill holes of small diameter whichare to be machined, since in this situation even a slight variation ofsuch spacing from zero results in major change in the clearance angle.In order to prevent such occurrence, the cutting tool disclosed in theEuropean prior publication has on its clamp component clamping surfacesat least to some extent converging toward each other, surfaces by meansof which the cutting tool may be secured on a processing machine, suchas one in the form of a lathe, it being possible to bring suchconverging surfaces in contact with correspondingly converging contactsurfaces of the tool holder. By means of the mould closure referred to aprecisely defined rotary position of the disclosed clasp tool may beachieved in that radial enlargement in the seating recess in the toolholder and the radial projection on the shaft component of the clasptool result, through the action of the clamping means, in rigorouslydefined application of the clamping surfaces of the radial projection tothe contact surfaces of the enlargement, change in the cutting positionperpendicular to the diametral advance plane when load is applied to thetool being prevented, since the rotary position of the cutting toolrelative to the tool holder is ensured in that application of theclamping surfaces to the application surface acts on a radius enlargedin relation to the radius of the receptacle bore.

[0003] In order to permit machining of drill holes of extremely smalldiameter, it has been recognized in the disclosed solution asadvantageous to configure the clasping tool as one piece. Otheradvantages to this end are achieved if the clasping tool consists of acutting alloy, since, because of the large elasticity modulus of cuttingalloy tools, the cutting edge remains precisely in the positionoriginally set even under relatively high loads, so that change in thecutting position relative to the diametral advance plane when a load isapplied is virtually eliminated.

[0004] It has been found, however, that, despite the measures described,the disclosed cutting tool approaches its limits when drill holes ofextremely small diameter, less than one millimeter, such as 0.7 mm, areto be machined. Despite the advantageous tool holding, the integratedconfiguration of the tool, and its construction by use of cutting alloymaterials, these disclosed measures do not make it possible to advancein this range of operation with boring diameters smaller than 1 mm toachieve the machining qualities desired.

[0005] EP-A-0 947 267 discloses a generic tool having a holder in whicha plate with three cutting edges may be secured by means of a threadedconnection. The free end of the holder on which the cutting tool may beseated has recesses by means of which reinforcing ribs are produced sothat, despite the holder components reduced by the cut-out recesses,such good reinforcement is obtained for the cutting plate thatvibrations impairing the machining quality during machining are absorbedand the holder is reinforced. Because of the flat application of theplate with three cutting edges on the end of the holder and thedisclosed possibility of fastening by means of a screw connection,misadjustment of the machining edge may occur and in addition theconfiguration of the disclosed solution is so large that application ofthis for drill holes of extremely small diameter is not possible.

[0006] On the basis of this state of the art the object of the inventionaccordingly is to improve the conventional cutting tool for the purposeof making it possible, while retaining the advantages of this tool, tomachine drill holes of extremely small diameters, such as onesappreciably smaller than 1 mm, while maintaining high quality standards.It is claimed for the invention that this object is attained by thecombination of characteristics specified in current claim 1.

[0007] A high degree of reinforcement is achieved for the neck componentof the cutting tool and the cutting component with cutting edge mountedon its free end is achieved in that, as specified in the preamble ofclaim 1, the retaining component has, extending transversely to theplane of the cutting edge, two reinforcing components such asreinforcing ribs which taper as they converge in the direction of thecutting component are positioned diametrically opposite each other inrelation to the retaining component, and assume their greatest width atthe point of their transition to the shank component. In the case of aconventionally designed retainer the reinforcing ribs of the cuttingcomponent permit sure absorption of the machining forces introduced intothe cutting component by way of the retaining component into the shankcomponent and then into the holding component to be associated with themachine. In particular, the reinforcing ribs counter vibrationsoccurring during machining with the cutting component and retain thelatter precisely in its required machining plane. Since the reinforcingribs extend perpendicular to the plane of the cutting component with itscutting edge, they occupy little structural space and, because of theirconvergent configuration, permit engagement of the cutting componentseven in drill holes of small diameter.

[0008] In that the reinforcing ribs preferably are obtained from theneck component by a grinding process from the neck component and alwayshave two different grinding patterns with different, preferably concave,radii of curvature in the direction of the cutting component, very highsupporting forces can be achieved for the cutting component and thestructural space required for the reinforcing ribs is optimized as well,so that a high degree of stiffening is achieved with geometrically smallreinforcing ribs, which thus permit engagement of the cutting componentalso in drill holes for a machining process whose diameter is smallerthan 1 mm, and 0.7 mm in particular.

[0009] Other advantageous embodiments of the cutting tool claimed forthe invention are specified in the additional dependent claims.

[0010] The invention in its additional advantageous embodiment isdescribed in detail in what follows with reference to an exemplaryembodiment, illustrated in a greatly enlarged diagram in the drawing, inwhich

[0011]FIG. 1 presents a perspective view of the cutting tool;

[0012]FIG. 2 a bottom view of the cutting tool shown in FIG. 1;

[0013]FIG. 3 an additionally enlarged view of a section of the front,head, part of the cutting tool shown in FIG. 1;

[0014]FIGS. 4 and 5 a section along line I-I and II-II respectively inFIG. 3.

[0015] The cutting tool illustrated in the figures is used in particularfor hollowing drill holes having a bore diameter <1 mm, preferably inthe area of 0.7 mm. The cutting tool has a clamping component 10 forsecuring the tool in tool holder not shown. Use may be made, forexample, of the tool holders as described in European Patent 0 385 280issued to the applicant. The side of the clamping component 10 facingaway from the tool holder is adjoined by a neck component 12 tapered inrelation to the clamping component 10, such neck component 12 havingintegral with it on its free end a cutting component 14 which isprovided at its extremity with a cutting edge 16 which adjoins a face 18of the cutting component 14 in the direction of the neck component 12.The direction of machining with the tool is indicated in FIGS. 1 to 3 byan arrow identified by an “X.”

[0016] As is to be seen in FIG. 2 in particular, the neck component 12has, extending along it, transversely to the plane with the cutting edge16, two reinforcing components in the form of two reinforcing ribs 20,22. The two reinforcing ribs 20, 22 taper convergently in the directionof the cutting component 14. In addition, the two reinforcing ribs 20,22 are positioned diametrically opposite each other relative to the neckcomponent 12, in particular in relation to the longitudinal axis 24 ofthe cutting tool. The neck component 12 extends more or less in rotationsymmetry around the longitudinal axis 24 in question and the tworeinforcing ribs 20, 22 extend like vanes on both sides of thelongitudinal axis 24 along the neck component 12. In addition, thereinforcing ribs 20, 22 reach their greatest width at the point of theirtransition to the clamping component 10, which may also be designatedshank or shank component of the cutting tool.

[0017] The two reinforcing ribs 20, 22, as well as the other geometricconfigurations of the cutting tool, are obtained in particular by agrinding process and the reinforcing ribs 20, 22 thus obtained from theneck component 12 each exhibits in the direction of the cuttingcomponent 14 two different grinding patterns with different, preferablyconcave, radii of curvature. In order to ensure a high degree ofengagement depth for the cutting edge 16, the grinding patterns selectedfor the two reinforcing ribs 20, 22 accordingly have greater curvaturein the direction of the cutting edge 16 than in the direction of theclamping component 10.

[0018] The free surface 26 of the cutting component 14, which issituated at the front end in the direction of machining X, is slantedbackward at an angle A, preferably 5°, from the vertical (see FIG. 2).The respective front free surface 26 of the cutting component is, inturn, itself slanted backward at an angle B, preferably 8° (see FIG. 3).As is also to be seen from FIG. 2, the face 18 in turn is slantedbackward at an angle C, preferably 5°, from the horizontal,specifically, in the direction of the clamping or shank component 10. Inaddition, the cutting edge 16 undergoes transition at its free end inthe direction of machining X to a supporting surface 28 (see FIG. 23)which extends parallel to the direction of machining X, the outercircumferential surface of this supporting surface 28 projecting beyondthe neck component 12 by an amount of excess E. Consequently, by itsexcess E the supporting surface and the cutting edge forms a kind ofhook tool relative to the neck component 12.

[0019] The illustrations in FIGS. 1 and 4 show that the clampingcomponent 10 has essentially two clamping surfaces 30 which convergetoward each other in the direction of the bottom 32 of the clampingcomponent 10 and which undergo transition to semicircular roofage 36. Inthis way the clamping component 10 may be secured in a correspondingseat of a clamping component by means of an adjusting screw not shown indetail. A clamping component such as this is described in greater detailin EP-B-0 385 280 and accordingly will not be discussed further at thispoint. In the area of the clamping component 10, which is bounded by thetwo clamping surfaces 30, a coolant feed channel 38 extends parallel tothe direction of machining X. A cooling lubricant in particular may befed by way of the coolant feed channel 38 in the direction of engagementof the cutting edge 16 with a tool to be machined (not shown). At thepoint at which the coolant feed channel 38 empties into the open, theneck component 12 is more greatly retracted relative to the clampingcomponent 10 (see FIG. 3) than on the diametrically opposite point inthe area of the top 34 of the cutting tool. A kind of domed support forthe cutting component 14 proper with its cutting edge 16 is produced onthe basis of the respective configuration, along with accompanyinggrinding patterns 23, 25 for the external outline of the cutting tool,at least in one diametral plane, as is illustrated in FIG. 2.

[0020] Hard alloys such as MG12, TN 35, TI25, or TF45 have been found tobe especially well suited. The cutting tool configuration alsoillustrated in the figures is that of a “right-hand” embodiment;mirror-image configuration of the figures presented yields acorresponding “left-hand” embodiment, should such prove to be necessaryfor the machining purpose pursued.

1. A cutting tool, in particular for hollowing drill holes, having aclamping component (10) for fastening the tool in a tool holder, theclamping component (10) having two clamping surfaces (30) which convergetoward each other in the direction of one side (32) of the clampingcomponent (10) and in the direction of the other side (34) of theclamping component (10) change in shape to that of roofage (36), and arod-shaped neck component (12) tapered in cross-section relative to theclamping component (10) adjoining on the side of the clamping component(10), the cutting component (14) being provided on its outer end with acutting edge (16) which is adjoined by a face (18) of the cuttingcomponent (14) in the direction of the neck component (12),characterized in that the neck component (12) has extending along ittransversely to the plane of the cutting edge (16) two reinforcingcomponents which, in the form of reinforcing ribs (20, 22) taper as theyconverge in the direction of the cutting component (14), suchreinforcing ribs (20, 22) being positioned diametrically opposite eachother in relation to the neck component (12) and assume their greatestwidth at the point of their transition to the clamping component (10).2. The cutting tool as claimed in claim 1, wherein the reinforcing ribs(20, 22) are obtained by a grinding process from the neck component (12)and exhibit two different grinding patterns (23, 25) with different,preferably concave, radii of curvature in the direction of the cuttingcomponent (14).
 3. The cutting tool as claimed in claim 2, wherein, inthe direction of the cutting neck (14), the grinding patterns (23, 25)selected for the reinforcing ribs (20, 22) exhibit greater curvaturethan in the direction of the clamping component (10).
 4. The cuttingtool as claimed in one of claims 1 to 3, wherein the free surface (26)of the cutting component (14), which is positioned on the foremost endin the direction of machining (X), is tilted backward from the verticalby an angle (A), preferably 5°.
 5. The cutting tool as claimed in claim4, wherein the foremost free surface (26) of the cutting component (14)is tilted backward from the cutting edge (16) by an additional angle(B), preferably 8°.
 6. The cutting tool as claimed in one of claims 1 to5, wherein the face (18) is tilted backward from the horizontal in thedirection of machining (X) by a third angle (C), preferably 5°.
 7. Thecutting tool as claimed in one of claims 1 to 6, wherein the free end ofthe cutting edge (16) becomes, in the direction of machining, asupporting surface (28) which extends parallel to the direction ofmachining (X) and projects beyond the neck component (12) by the amountof an excess (E).
 8. The cutting tool as claimed in one of claims 1 to7, wherein the clamping component (10) has two clamping surfaces (30)which converge toward each other in the direction of the bottom (32) ofthe clamping component (10) and change in shape to that of semicircularroofage (36) in the direction of the top (34) of the clamping component(10).
 9. The cutting tool as claimed in claim 8, wherein a coolant feedchannel (38) extends parallel to the direction of machining (X) in thearea of the clamping component (10) which is bounded by the two clampingsurfaces (30).
 10. The cutting tool as claimed in claim 9, wherein theneck component (12) recedes farther into the clamping component (10) asit undergoes transition to the latter, at the point at which the coolantfeed channel (38) empties into the open than on the diametricallyopposite side.